The present invention relates generally to vehicle sensor failure detection and, more specifically, to a system and method for detecting a failure in a vehicle speed sensor when the vehicle is also equipped with a vehicle position determination sensor.
Various types of electronic sensors are becoming more prevalent on vehicles, especially on fleets of vehicles wherein it is desirable to monitor certain information as a fleet vehicle covers a particular route. One type of sensor becoming common on these vehicles is a present vehicle position sensor, used to keep track of the geographic location of the vehicle in order to provide automated trip reporting and routing capabilities. This type of system is also becoming increasingly popular for use in automobile navigation systems. One of the most common systems of this type is a global positioning system (GPS) through which a receiver installed on the vehicle can receive information indicative of the present geographic position of the receiver, and hence the vehicle, by capturing signals transmitted over geostationary satellite.
In general, GPS systems are used to allow a receiver to determine its geographical position based upon signals received from multiple orbiting satellites. In navigational applications of GPS, the latitude, longitude and altitude of any point close to the surface of the earth can be calculated from the propagation times of electromagnetic energy transmitted from four or more satellites to the receiver location. In vehicular applications, the GPS system is electronically connected to a microprocessor-based controller installed on the vehicle, generally referred to as an on-board computer (OBC), which performs various navigational tasks with information received. While such systems work very well in providing intended navigational and other capabilities, the data obtained can also be used to accomplish additional functions, thereby making better use of the equipment and adding to its cost justification.
The system and method of the present invention further utilizes data obtained from a GPS receiver to detect failures in a vehicle's speed sensor. This sensor is typically a speedometer or other sensing device which provides a signal indicative of the vehicle's velocity or acceleration. By electronically connecting both the speed sensor and GPS receiver to the vehicle's OBC, the distance traveled by the vehicle according to information obtained from the speed sensor can be compared to distance measurements obtained through the GPS position sensor. Discrepancies between the measurements can be used to indicate sensor faults and/or failures.
In accordance with the present invention, a vehicle's geographic position is obtained with a GPS or other similar position determining system. Once a predetermined amount of time has expired, a vehicle speed is obtained from the speed sensor and a second geographic position is determined. A set of distance calculations are then made, the first by multiplying the speed measurement by the predetermined time period. The second distance measurement is made by finding the linear distance between the last two position points obtained by the position determining system. If these distance measurements fall within a predetermined tolerance of one another, it can be assumed that the speed sensor is functioning properly. Wide discrepancies, however, indicate some type of system error such as a speed sensor failure. Conversely, if the speed sensor is determined to be functioning properly, there may be errors in the position sensing system.
Therefore, the present invention allows speed sensor systems to be monitored for failure without requiring any additional hardware to be implemented on the vehicle. The speed and position data obtained can also be used to provide calibration data for the various sensing devices, thereby providing an inherent redundancy in these systems and maximizing the cost efficiency as well as usefulness of an on-board vehicle position determining system.
These and other features and advantages of the present invention will become apparent to one of skill in the art upon review of the following description, taken in conjunction with the accompanying drawings.